Class VariableInfo
- java.lang.Object
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- jakarta.servlet.jsp.tagext.VariableInfo
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public class VariableInfo extends Object
Information on the scripting variables that are created/modified by a tag (at run-time). This information is provided by TagExtraInfo classes and it is used by the translation phase of JSP.Scripting variables generated by a custom action have an associated scope of either AT_BEGIN, NESTED, or AT_END.
The class name (VariableInfo.getClassName) in the returned objects is used to determine the types of the scripting variables. Note that because scripting variables are assigned their values from scoped attributes which cannot be of primitive types, "boxed" types such as
java.lang.Integer
must be used instead of primitives.The class name may be a Fully Qualified Class Name, or a short class name.
If a Fully Qualified Class Name is provided, it should refer to a class that should be in the CLASSPATH for the Web Application (see Servlet 2.4 specification - essentially it is WEB-INF/lib and WEB-INF/classes). Failure to be so will lead to a translation-time error.
If a short class name is given in the VariableInfo objects, then the class name must be that of a public class in the context of the import directives of the page where the custom action appears. The class must also be in the CLASSPATH for the Web Application (see Servlet 2.4 specification - essentially it is WEB-INF/lib and WEB-INF/classes). Failure to be so will lead to a translation-time error.
Usage Comments
Frequently a fully qualified class name will refer to a class that is known to the tag library and thus, delivered in the same JAR file as the tag handlers. In most other remaining cases it will refer to a class that is in the platform on which the JSP processor is built (like Jakarta EE). Using fully qualified class names in this manner makes the usage relatively resistant to configuration errors.
A short name is usually generated by the tag library based on some attributes passed through from the custom action user (the author), and it is thus less robust: for instance a missing import directive in the referring JSP page will lead to an invalid short name class and a translation error.
Synchronization Protocol
The value of the `scope` attribute does not affect the visibility of the variables within the generated program. It affects where and thus for how long there will be additional references to the object denoted by the variable.
The result of the invocation on getVariableInfo is an array of VariableInfo objects. Each such object describes a scripting variable by providing its name, its type, whether the variable is new or not, and what its scope is. Scope is best described through a picture:
The JSP 2.0 specification defines the interpretation of 3 values:
- NESTED, if the scripting variable is synchronized with the calling page between the start tag and the end tag of the action that defines it.
- AT_BEGIN, if the scripting variable is synchronized with the calling page from the start tag of the action that defines it until the end of the scope.
- AT_END, if the scripting variable is synchronized with the calling page after the end tag of the action that defines it until the end of the scope.
Variable Synchronization Points Variable Synchronization Points
doStartTag() doInitBody() doAfterBody() doEndTag() doTag() Tag
AT_BEGIN, NESTED
AT_BEGIN, AT_END
IterationTag
AT_BEGIN, NESTED
AT_BEGIN, NESTED
AT_BEGIN, AT_END
BodyTag
AT_BEGIN, NESTED1
AT_BEGIN, NESTED1
AT_BEGIN, NESTED
AT_BEGIN, AT_END
SimpleTag
AT_BEGIN, AT_END
doStartTag()
ifEVAL_BODY_INCLUDE
is returned, or afterdoInitBody()
otherwise.Variable Information in the TLD
Scripting variable information can also be encoded directly for most cases into the Tag Library Descriptor using the <variable> subelement of the <tag> element. See the JSP specification.
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Field Summary
Fields Modifier and Type Field Description static int
AT_BEGIN
Scope information that scripting variable is synchronized with the calling page after start tag.static int
AT_END
Scope information that scripting variable is synchronized with the calling page after end tag.static int
NESTED
Scope information that scripting variable is synchronized with the calling page only within the start/end tags.
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Constructor Summary
Constructors Constructor Description VariableInfo(String varName, String className, boolean declare, int scope)
Constructor These objects can be created (at translation time) by the TagExtraInfo instances.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description String
getClassName()
Returns the type of this variable.boolean
getDeclare()
Returns whether this is a new variable.int
getScope()
Returns the synchronization scope of the variable.String
getVarName()
Returns the name of the scripting variable.
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Field Detail
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NESTED
public static final int NESTED
Scope information that scripting variable is synchronized with the calling page only within the start/end tags.- See Also:
- Constant Field Values
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AT_BEGIN
public static final int AT_BEGIN
Scope information that scripting variable is synchronized with the calling page after start tag.- See Also:
- Constant Field Values
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AT_END
public static final int AT_END
Scope information that scripting variable is synchronized with the calling page after end tag.- See Also:
- Constant Field Values
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Constructor Detail
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VariableInfo
public VariableInfo(String varName, String className, boolean declare, int scope)
Constructor These objects can be created (at translation time) by the TagExtraInfo instances.- Parameters:
varName
- The name of the scripting variableclassName
- The type of this variabledeclare
- If true, it is a new variable (in some languages this will require a declaration)scope
- Indication of the synchronization scope of the variable
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Method Detail
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getVarName
public String getVarName()
Returns the name of the scripting variable.- Returns:
- the name of the scripting variable
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getClassName
public String getClassName()
Returns the type of this variable.- Returns:
- the type of this variable
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getDeclare
public boolean getDeclare()
Returns whether this is a new variable. If so, in some languages this will require a declaration.- Returns:
- whether this is a new variable.
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